1. Field of the Invention:
The present invention relates generally to a method of manufacturing a capacitor in a semiconductor device. More particularly, the present invention relates to a method of manufacturing a capacitor in a semiconductor device capable of improving the characteristic of a Ta2O5 film, by performing a plasma process in in-situ under the mixture gas atmosphere of nitrogen and oxygen during deposition of CVD Ta2O5 film used as a dielectric film of a capacitor.
2. Description of the Prior Arts:
A tantalum oxide film (Ta2O5) is higher 5 times in the dielectric constant than the ONO film (Oxide-Nitride-Oxide) used as a dielectric film of a capacitor in the process of manufacturing the existing DRAM. Thus, it has been widely attracted as dielectric materials of a capacitor in the process of manufacturing a DRAM that requires the integration degree of more than 1Giga byte. In particular, Ta2O5 can represent the high step coverage by CVD process. Also, it can be implemented as a small film having a good dielectric characteristic and a less leak current by a subsequent annealing process.
It has been reported that the cell capacitance of the capacitor, which uses the Ta2O5 film having a MIS (Metal-Insulator-Semiconductor) structure as a dielectric film, is more than 3fF since the underlying polysilicon plug was crowded, and also the cell leak current of the capacitor is less than 1fF.
In order to improve the integration degree, focus has been centered to developing a capacitor that uses as a dielectric film the Ta2O5 film of a MIM (Metal-Insulator-Metal) structure using a metal layer as a lower electrode. The reason is that, if the Ta2O5 film is formed on the metal electrode, the crystallization of the Ta2O5 film can be improved to increase its dielectric constant, and also the leak current of the Ta2O5 film is advantageous since the work function of the metal layer is high.
The CVD Ta2O5 film may include organic impurities and are amorphous. Thus, it cannot be used intact without improving the quality of the film by a subsequent process. The subsequent process for improving the quality of the film may include a low temperature process and a high temperature process. Then, the low temperature uses a plasma process for removing an organic source within the Ta2O5 film under oxidization atmosphere and a UV/O3 process. The high temperature uses a rapid annealing process for improving crystallization of the thin film etc. When processing the MIM Ta2O5 film, if the process temperature is increased under oxidization atmosphere, a metal oxide may be formed at the interface of the lower metal electrode and the Ta2O5 film. Thus metal oxide may increase the equivalent oxide thickness to decrease the amount of charging charges. Thereby, as the sufficient amount of charging charges cannot be obtained at the operating voltage within the unit cell, it may not be used as a capacitor to storing data.
It is therefore an object of the present invention to provide a method of manufacturing a capacitor in a semiconductor device capable of improving the characteristic of a Ta2O5 film while prohibiting forming an oxide film of the lower electrode.
In order to accomplish the above object, the method of manufacturing a capacitor in a semiconductor device according to the present invention is characterized in that it comprises the steps of forming a polysilicon film on a semiconductor substrate in which a given underlying structure is formed; sequentially forming a first buffer layer and a metal layer on the polysilicon film to form a lower electrode; forming a Ta2O5 film on the metal layer, wherein the process of depositing the Ta2O5 film is performed by a plasma process under the mixture gas atmosphere of nitrogen and oxygen; and forming a second buffer layer and an upper electrode on the Ta2O5 film.